Chemical conversion bath replenishment method

ABSTRACT

The purpose of the present invention is to provide a method for replenishing an aluminum metal chemical conversion bath, the method being capable of maintaining the corrosion resistance and coating film adhesiveness of the chemical conversion coating formed even if the aluminum metal chemical conversion bath is used continuously. Provided is a method for replenishing an aluminum metal chemical conversion bath with a replenishing agent, wherein the replenishing agent comprises a zirconium salt and/or a titanium salt and an effective fluoride, and the replenishing agent is supplied so that the ratio F/Al of the fluorine ion concentration (mg/L) with respect to the aluminum ion concentration (mg/L) in the aluminum metal chemical conversion bath is 1.8-4.5.

TECHNICAL FIELD

The present invention relates to methods for replenishing chemical conversion baths.

BACKGROUND ART

Conventionally, various nonchromate treatment methods have been proposed for the surface treatment of aluminum and an aluminum alloy. For example, an aluminum metal surface treatment bath is proposed which contains at least one kind of phosphoric acid, condensed phosphoric acid or salts thereof; at least one kind of a zirconium salt or a titanium salt; an effective fluoride; at least one kind of phosphorous acid, hypophosphoric acid or salts thereof, each at a prescribed amount, and also proposed is a surface treatment method using such a treatment bath (for example, see Patent Document 1 mentioned later). According to such a treatment bath and treatment method, the surface of the aluminum and the aluminum alloy can be provided with chemical conversion coatings having both corrosion resistance and coating film adhesiveness.

The chemical conversion treatment of the aluminum and its alloy according to the treatment bath and the treatment method indicated in Patent Document 1 generally includes a step of continuously conveying treatment targets to the treatment bath to soak the targets in the treatment bath or allow the targets to undergo spraying of the treatment bath. During the process of such a chemical conversion treatment, active ingredients of the treatment bath are consumed and with it the composition of components in the treatment bath varies. For example, during the chemical conversion treatment reaction, the etching by fluorine of the substrate surface to eliminate aluminum gradually increases the relative concentration of aluminum in the treatment bath, eventually causing an aluminum sludge.

Thus, continuing to use the treatment bath with no countermeasures taken results in some cases where the chemical conversion coatings formed fail to exhibit intended effects such as corrosion resistance. A way to address such a problem will be replenishing the treatment bath with a replenishing agent containing active ingredients at a certain interval. Such a way, however, cannot necessarily maintain the concentration of active ingredients of the treatment bath at a certain level. For example, there are some cases where aluminum and its alloy that have undergone the chemical conversion treatment is subjected to some processes and thereafter again subjected to a chemical conversion treatment. In those cases, portions of the aluminum and its alloy that have already undergone the chemical conversion treatment fail to have the progress of the reaction, with a result that the amount of the active ingredients to be consumed is relatively low. In other words, the treatment time and the amount of the active ingredients to be consumed are not necessarily proportional to each other. Another problem is the varying composition of components in the treatment bath, as described above. In this way, conventional methods involving the continuous chemical conversion treatment with a treatment bath have been unable to achieve the stable formation of chemical conversion coatings that exhibit such properties as corrosion resistance.

Patent Document 1: Japanese Unexamined Patent Application, Publication No. H09-143752

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present inventors have extensively considered the relation between proportions of components present in the chemical conversion bath and the resultant chemical conversion coatings. Consequently, they have found out that controlling a ratio between an aluminum ion concentration and a fluorine ion concentration in the chemical conversion bath so as to be in a certain range would result in forming chemical conversion coatings having both corrosion resistance and coating film adhesiveness.

It is therefore an object of the present invention to provide a method for replenishing an aluminum metal chemical conversion bath that by keeping the ratio between the aluminum ion concentration and the fluorine ion concentration in the chemical conversion bath so as to be in a certain range, is capable of maintaining the corrosion resistance and coating film adhesiveness of chemical conversion coatings formed even when the aluminum metal chemical conversion bath is continuously used.

Means for Solving the Problems

The present invention, in order to accomplish the above-mentioned object, provides a method for replenishing an aluminum metal chemical conversion bath with a replenishing agent, wherein the replenishing agent comprises a zirconium salt and/or a titanium salt, and an effective fluoride, and wherein the replenishing agent is supplied so that the ratio F/Al of the fluorine ion concentration (mg/L) with respect to the aluminum ion concentration (mg/L) in the aluminum metal chemical conversion bath is 1.8 to 4.5.

Preferably, the replenishing agent further comprises at least one kind selected from the group consisting of phosphoric acid, phosphorous acid and hydrogen peroxide.

Preferably, the aluminum metal chemical conversion bath comprises a zirconium salt and/or a titanium salt; an effective fluoride; at least one kind selected from the group consisting of phosphoric acid, condensed phosphoric acid and salts thereof; and at least one kind selected from the group consisting of phosphorous acid, hypophosphoric acid and salts thereof.

Preferably, the replenishing agent is supplied such that the chemical conversion bath has a pH in a prescribed range so as to give the F/Al ranging from 1.8 to 4.5.

Preferably, the replenishing agent is supplied such that the chemical conversion bath has an electric conductivity in a prescribed range so as to give the F/Al ranging from 1.8 to 4.5.

Preferably, a treatment target of the aluminum metal chemical conversion bath is an aluminum beverage can.

Effects of the Invention

The present invention provides a method for replenishing an aluminum metal chemical conversion bath that is capable of maintaining the corrosion resistance and coating film adhesiveness of chemical conversion coatings formed even if the aluminum metal chemical conversion bath is continuously used.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to embodiments described below. The aluminum metal chemical conversion bath, to which the replenishment method according to an embodiment of the present invention is applied, is employed to provide an aluminum substrate formed of an aluminum metal with a protecting coating superior in properties including appearance, corrosion resistance and coating film adhesiveness.

<Chemical Conversion Bath>

The aluminum metal chemical conversion bath (hereinafter, referred to as the “chemical conversion bath” in some cases), to which the replenishment method according to an embodiment of the present invention is applied, is obtained by diluting, with an adequate amount of water, a chemical conversion agent composition comprising a zirconium salt and/or a titanium salt; an effective fluoride; at least one kind selected from the group consisting of phosphoric acid, condensed phosphoric acid and salts thereof (hereinafter referred to as the “phosphoric acid and others” in some cases); and at least one kind selected from the group consisting of phosphorous acid, hypophosphoric acid and salts thereof (hereinafter referred to as the “phosphorous acid and others” in some cases).

According to the chemical conversion bath of an embodiment of the present invention, an aluminum substrate surface is provided with a chemical conversion coating superior in such properties as corrosion resistance. Specifically, first, the effective fluoride, contained in the chemical conversion bath, etches the aluminum substrate surface to eliminate oxide coatings therefrom. The phosphorous acid and others function as reducing agents that prevent the oxidization of the etched aluminum substrate surface. The zirconium salt and/or titanium salt, the effective fluoride, the phosphoric acid and others, and the phosphorous acid and others, form double salts, which then provide the aluminum substrate surface with a solid chemical conversion coating.

[Zirconium Salt]

The zirconium salt that is a component of the chemical conversion bath according to an embodiment of the present invention is not particularly limited, with its examples including lithium, sodium, potassium and ammonium salts of zirconium hydrofluoric acid (H₂ZrF₆) and fluorozirconic acid (Li₂ZrF₆, Na₂ZrF₆, K₂ZrF₆, (NH₄)₂ZrF₆), zirconium sulfate (Zr(SO₄)₂), zirconyl sulfate (ZrO(SO₄)), zirconium nitrate (Zr(NO₃)₄), zirconyl nitrate (ZrO(NO₃)₂), zirconium acetate, and zirconium fluoride (ZrF₄). Those may be used singly or more than one may be combined.

[Titanium Salt]

The titanium salt that is a component of the chemical conversion bath according to an embodiment of the present invention is not particularly limited, with its examples including lithium, sodium, potassium and ammonium salts of titanium hydrofluoric acid and fluorotitanic acid (Li₂TiF₆, Na₂TiF₆, K₂TiF₆, (NH₄)₂TiF₆), titanium sulfate (Ti(SO₄)₂), titanyl sulfate (TiO(SO₄)), titanium nitrate (Ti(NO₃)₄), titanine nitrate(TiO(NO₃)₂), and titanium fluoride (TiF₃.TiF₄). Those may be used singly or more than one may be combined.

The zirconium salt and/or titanium salt are preferably contained in an amount, in terms of metal, of 10 ppm or more in the chemical conversion bath according to an embodiment of the present invention, more preferably 10 to 500 ppm, much more preferably 10 to 100 ppm. The addition at the concentration, in terms of metal, of the zirconium salt and/or titanium salt in the chemical conversion bath which is less than 10 ppm would lead to almost no formation of the chemical conversion coating. Conversely, the addition even at the concentration, in terms of metal, of the zirconium salt and/or titanium salt in the treatment bath that is 500 ppm or more would fail to realize beneficial effects. In view thereof, the concentration, in terms of metal, of the zirconium salt and/or titanium salt is preferably not more than 500 ppm.

[Effective Fluoride]

The effective fluoride is a fluoride that liberates fluorine ions in the chemical conversion bath. The effective fluoride that is a component of the chemical conversion bath according to an embodiment of the present invention is not particularly limited, with its examples including hydrofluoric acid (HF), ammonium fluoride (NH₄F), ammonium hydrogen fluoride (NH₄HF₂), sodium fluoride (NaF), and sodium hydrogen fluoride (NaHF₂). Those may be used singly or more than one may be combined.

In the chemical conversion bath according to an embodiment of the present invention, fluorine ions (F⁻) are liberated from the effective fluoride. Fluorine ions etch the aluminum substrate surface to eliminate oxide coatings, and moreover inhibit the precipitation of zirconium phosphate generated in the chemical conversion bath. In addition, by the fluorine ions, the aluminum that has eluted into the chemical conversion bath during the chemical conversion treatment of the aluminum substrate is caused to dissolve as fluoroaluminum into the chemical conversion bath thereby inhibiting the formation of an aluminum sludge.

In the chemical conversion bath according to an embodiment of the present invention, preferably, the concentration (mg/L) of fluorine ions that is expressed as its ratio with respect to the concentration (mg/L) of aluminum ions that have eluted into the chemical conversion bath as a result of the chemical conversion treatment reaction, i.e., F/Al, is 1.8 to 4.5. The F/Al of 1.8 or more, which means the aluminum ions being sufficiently soluble in the chemical conversion bath, ensures an enhanced uniformity of the chemical conversion coating formed on the aluminum substrate surface. The F/Al of 4.5 or less, which means the inhibition of the etching by fluorine ions from being excessive, ensures the formation of a chemical conversion coating that exhibits a sufficient corrosion resistance on the aluminum substrate surface. The F/Al is preferably 1.8 to 2.2. The aluminum ion concentration is measurable by ICP (inductively coupled plasma spectroscopy). The fluorine ion concentration is measurable by ion chromatography.

[Phosphoric Acid and Others]

The phosphoric acid and salts thereof that are components of the chemical conversion bath according to an embodiment of the present invention are not particularly limited, with their examples including alkali metal salts of phosphoric acid, such as H₃PO₄, (NH₄)H₂PO₄, NaH₂PO₄ and KH₂PO₄, and alkali earth metal salts of phosphoric acid, such as calcium phosphate and magnesium phosphate. The condensed phosphoric acid and salts thereof that are components of the chemical conversion bath according to an embodiment of the present invention are not particularly limited. Examples of the condensed phosphoric acid include pyrophosphoric acid, tripolyphosphoric acid, metaphosphoric acid and ultraphosphoric acid. Examples of the condensed phosphoric acid salts include salts of alkali metals such as sodium and potassium, salts of alkali earth metals such as calcium and magnesium; and ammonium salts. Those may be used singly or more than one may be combined.

Preferably, the phosphoric acid and others are contained in an amount, in terms of phosphoric acid, of 10 ppm or more in the chemical conversion bath according to an embodiment of the present invention, more preferably 10 to 500 ppm, much more preferably 10 to 100 ppm. If the concentration, in terms of phosphoric acid, of the phosphoric acid and others in the chemical conversion bath according to an embodiment of the present invention is less than 10 ppm, blackening in boiling water is encountered. Conversely, if the concentration, in terms of phosphoric acid, of the phosphoric acid and others in the chemical conversion bath is more than 500 ppm, blackening in boiling water is encountered and coating film adhesiveness is worsened.

[Phosphorous Acid and Others]

The phosphorous acid, hypophosphoric acid and salts thereof that are components of the chemical conversion bath according to an embodiment of the present invention are not particularly limited, with their examples including phosphorous acid and hypophosphoric acid, and their salts, such as salts of alkali metals including sodium and potassium, salts of alkali earth metals including calcium and magnesium, ammonium salts. Those may be used singly or more than one may be combined.

Preferably, the phosphorous acid and others are contained in an amount, in terms of phosphorous acid, of 10 ppm or more in the chemical conversion bath according to an embodiment of the present invention, more preferably 10 to 5000 ppm, much more preferably 50 to 500 ppm. If the concentration, in terms of phosphorous acid, of the phosphorous acid and others in the chemical conversion bath according to an embodiment of the present invention is less than 10 ppm, the uniformity of the chemical conversion coating is insufficient. Conversely, if the concentration, in terms of phosphorous acid, of the phosphorous acid and others in the chemical conversion bath is 5000 ppm or more, the coating film adhesiveness is decreased.

The chemical conversion bath of an embodiment of the present invention may further contain, as needed, antibacterial agents, surfactants rust-preventive agents, and others. Examples of the antibacterial agents include alcohols such as ethanol and isopropanol; guanidine group-containing compounds such as polyhexamethylene biguanidine hydrochloride; benzimidazole-based antibacterial agents such as 2-(4-tiazolyl)-benzimidazole and methyl-2-benzimidazolecarbamate; phenol-based antibacterial agents such as p-chloro-m-xylenol and p-chloro-m-cresol; nitrile-based antibacterial agents such as 2,4,5,6-tetrachloroisophthalonitrile and 1,2-dibromo-2,4-dicyanobutane; pyridine-based antibacterial agents such as (2-pyridylthio-1-oxide)sodium and bis(2-pyridylthio-1-oxide)zinc; isothiazolone-based antibacterial agents such as 2-methyl-4-isothiazoline-3-one and 5-chloro-2-methyl-4-isothiazoline-3-one; quaternary ammonium salts such as benzalkonium chloride and benzethonium chloride; benzoic acid, ethyl p-oxybenzoate, sorbic acid, potassium sorbate, sodium dehydroacetate, and sodium propionate. Examples of the surfactants include nonionic surfactants, cationic surfactants and anionic surfactants. Examples of the rust-preventive agents include tannic acid, imidazoles, triazines, guanines, hydrazines, and biguanide. Other examples that may be added to the chemical conversion bath are those aimed at enhancing the adhesiveness, which may be silane coupling agents, colloidal silica, amines, and phenol resin-containing water-soluble organic compounds.

The pH at 25° C. of the chemical conversion bath according to an embodiment of the present invention is preferably 2 to 4, more preferably 2.5 to 3.5. If the pH of the chemical conversion bath is less than 2, which leads to excessive etching, the formation of the chemical conversion coating is difficult and there are decreases in the boiling water blackening resistance and in the coating film adhesiveness. Conversely, if the pH of the chemical conversion bath exceeds 4, the cloudiness and the sludge are produced in the chemical conversion bath, the formation of the chemical conversion coating is difficult, and there is decrease in the boiling water blackening resistance.

A treatment target of the chemical conversion bath according to an embodiment of the present invention is an aluminum substrate, with an aluminum metal of the aluminum substrate being not particularly limited. Examples thereof include aluminum, aluminum-copper alloy, aluminum-manganese alloy, aluminum-silicon alloy, aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, aluminum-zinc alloy, and aluminum-zinc-magnesium alloy. The shape of the aluminum substrate that is a treatment target is not particularly limited, and the aluminum substrate with any shape, including a plate, a rod, and a can, may be subjected to the chemical conversion treatment. More specifically, preferable chemical conversion treatment targets of the aluminum metal chemical conversion bath according to an embodiment of the present invention may be 3000-type alloy aluminum beverage cans.

According to the chemical conversion bath according to an embodiment of the present invention, the aluminum substrate surface is provided with a uniform chemical conversion coating. Consequently, the chemical conversion coating, even after its thinning, still maintains corrosion resistance, and therefore exhibits an enhanced adhesiveness. For instance, an aluminum beverage can that has had the chemical conversion coating is subjected to a rigorous drawing process, which means the chemical conversion coating is required to have not just corrosion resistance but also adhesiveness. The chemical conversion bath according to an embodiment of the present invention is preferably used in such uses as aluminum beverage cans as well.

<Replenishing Agent>

The replenishing agent that is used in the method for replenishing an aluminum metal chemical conversion bath comprises a zirconium salt and/or a titanium salt, and an effective fluoride, and preferably further comprises at least one kind selected from the group consisting of phosphoric acid, phosphorous acid and hydrogen peroxide.

The zirconium salt and/or titanium salt, the effective fluoride, the phosphoric acid and the phosphorous acid are components that by forming double salts produce the chemical conversion coating, and therefore are come to be consumed toward the formation of the chemical conversion coating. Fluorine ions are liberated from the effective fluoride, and together with aluminum ions that have eluted into the chemical conversion bath, form such components as fluoroaluminum, resulting in being consumed. The phosphorous acid, which serves as a reducing agent that prevents the oxidization of the aluminum substrate surface that has been etched by fluorine, oxidizes itself to lose the functioning of the reducing agent. Thus, allowing those components to be contained in the replenishing agent, which is then supplied to the chemical conversion bath, is necessary to realize the continuous use of the chemical conversion bath.

The zirconium salt that is a component of the replenishing agent according to an embodiment of the present invention, which is not particularly limited, may be, for example, the zirconium salt contained in the above-mentioned chemical conversion bath according to an embodiment of the present invention. Likewise, the titanium salt, the effective fluoride, the phosphoric acid, and the phosphorous acid may be, for example, the effective fluoride, the phosphoric acid and others, and the phosphorous acid and others that are contained in the above-mentioned chemical conversion bath according to an embodiment of the present invention.

The replenishing agent according to an embodiment of the present invention may contain a pH regulator in order to regulate pH in the chemical conversion bath. The pH regulator is not particularly limited with its examples including general acids and alkalis such as nitric acid and ammonia.

As in the case with the chemical conversion bath, the replenishing agent according to an embodiment of the present invention may contain, as needed, antibacterial agents, surfactants, rust-preventive agents and others.

<Replenishment Method>

The method for replenishing an aluminum metal chemical conversion bath, which uses the replenishing agent according to an embodiment of the present invention, will be described. The replenishment method according to an embodiment of the present invention is performed by supplying the above-mentioned replenishing agent such that the ratio between the concentration (mg/L) of aluminum ions that have eluted into the chemical conversion bath as a result of the aluminum metal being etched by fluorine and the concentration (mg/L) of fluorine ions in the chemical conversion bath, i.e., F/Al, is 1.8 to 4.5.

The increase in the aluminum ion concentration in the chemical conversion bath is brought about by the aluminum metal etching by fluorine in the chemical conversion bath. The increase in the aluminum ion concentration would cause an aluminum sludge. Aluminum ions that would bond with fluorine ions are converted to fluoroaluminum, which is soluble. In view thereof, the presence of an adequate amount of fluorine ions relative to aluminum ion would prevent the aluminum sludge. The increase in the fluorine ion concentration in the chemical conversion bath, which would lead to an excessive etching by fluorine ions, would inhibit the formation of the chemical conversion coating. And yet, the bonding between aluminum ions and fluorine ions to give fluoroaluminum would suppress the etching by the fluorine ions. In view thereof, the presence of an adequate amount of aluminum ions relative to fluorine ions would suppress the excessive etching by fluorine ions. Hence, it is important for the ratio of the fluorine ion concentration with respect to the aluminum ion concentration in the chemical conversion bath to be maintained to be within the above-mentioned range. The F/Al of 1.8 or more, which means the aluminum ions being sufficiently soluble in the chemical conversion bath, ensures an enhanced uniformity of the chemical conversion coating formed on the aluminum substrate surface, which is thus preferable. The F/Al of 4.5 or less, which means the inhibition of the etching by fluorine ions from being excessive, ensures the formation of a chemical conversion coating with a sufficient corrosion resistance on the aluminum substrate surface. The F/Al is preferably 1.9 to 2.1.

In the replenishment method according to an embodiment of the present invention, the replenishing agent is supplied such that the pH at 25° C. in the chemical conversion bath is 2 to 4. If the pH at 25° C. in the chemical conversion bath is less than 2, which means an increased etching with respect to the aluminum substrate, an increased aluminum ion concentration results. Similarly, if the pH exceeds 4, which means a decreased concentration of aluminum ions that can be soluble, a decreased aluminum ion concentration results. Thus, keeping the pH in the above-mentioned range leads to maintaining the aluminum ion concentration in the chemical conversion bath within a certain range, which makes it easy for F/Al to be controlled within the preferred range. The pH measurement method is not particularly limited, and may involve the use of e.g., commercially-available pH electrodes.

In the addition of the replenishing agent according to an embodiment of the present invention such that the pH is kept within the above-mentioned range so as to eventually give F/Al kept ranging from 1.8 to 4.5, it is preferred to control the content and pH of components, such as the effective fluoride, of the replenishing agent.

In the replenishment method according to an embodiment of the present invention, the replenishing agent is supplied such that the electric conductivity at 25° C. in the chemical conversion bath is 0.5 to 5 mS/cm. As described above, the continuous use of the chemical conversion bath leads to the consumption of the coating-forming components of the chemical conversion agent, which are the zirconium salt, the titanium salt, the effective fluoride, the phosphoric acid and others, and the phosphorous acid and others, resulting in decreased ion concentration in the chemical conversion bath. This decreases the electric conductivity in the chemical conversion bath. Thus, keeping the electric conductivity in the above-mentioned range enables controlling the concentration of the coating-forming components of the chemical conversion bath in a certain range. The electric conductivity measurement method is not particularly limited, and may involve the use of e.g., commercially-available EC electrodes.

In the addition of the replenishing agent according to an embodiment of the present invention such that the electric conductivity is kept in the above-mentioned range so as to eventually give F/Al kept ranging from 1.8 to 4.5, it is preferred to control factors such as the content of the components, such as the effective fluoride, of the replenishing agent.

The replenishing agent according to an embodiment of the present invention may be supplied in a manner which is not particularly limited, but is preferably supplied as required in a small amount in such a manner as will not significantly vary the composition of the components in the chemical conversion bath. For instance, it is preferred for the supply amount to be automatically controlled such that the pH and the electric conductivity are kept within a certain range depending on detected values of the above-mentioned pH electrodes and EC electrodes.

According to the above-described replenishment method of an embodiment of the present invention, even in the continuous use of the chemical conversion bath that can involve the changes of components in the chemical conversion bath, maintaining the chemical conversion bath so as to have F/Al of 1.8 to 4.5 leads to providing the aluminum substrate surface with a uniform chemical conversion coating. Therefore, the chemical conversion bath to which the replenishment method of an embodiment of the present invention is applied enables the suitable chemical conversion treatment of, for example, aluminum beverage cans, for which the adhesiveness as well as the corrosion resistance of the chemical conversion coatings are demanded.

<Chemical Conversion Method>

Next, a chemical conversion method for an aluminum metal that uses the chemical conversion bath according to an embodiment of the present invention will be described. The chemical conversion treatment is preceded by the pretreatment of the aluminum substrate. For instance, aluminum cans, such as beverage cans, are produced through processes including a drawing process named drawing/ironing process (hereinafter referred to as the “DI processing”), their surfaces having the adhering of aluminum powder called smut and lubricating oil produced during those processes. In addition, the aluminum substrate surfaces are generally coated with oxide coatings to be passivated. In view thereof, the removal of that smut and lubricating oil by means of e.g., alkali treatment and acid treatment as well as the adequate etching of the aluminum substrate surface are preferred. Performing such alkali treatment and acid treatment as the pretreatment could provide the aluminum substrate surface with a solid chemical conversion coating.

The chemical conversion method for the aluminum metal, which is not particularly limited, is performed by soaking an aluminum product or the like, which is a treatment target, in the chemical conversion bath, or by spraying or applying the chemical conversion agent composition in the chemical conversion bath. The time necessary for the chemical conversion treatment, which differs depending on the chemical conversion agent composition according to the chemical conversion bath, the treatment temperature, and treatment method, is generally 5 to 60 seconds.

In the chemical conversion method according to an embodiment of the present invention, the temperature of the chemical conversion bath is preferably from room temperature to 60° C., more preferably from 30 to 50° C. In the case of the chemical conversion bath with a temperature lower than room temperature (e.g., 25° C.), the formation of the chemical conversion coating makes progress at a lower speed and the attempt to form the coating at a higher speed would require a higher concentration of components of the treatment bath; either case is economically disadvantageous. Conversely, in the case of the chemical conversion bath with a temperature higher than 60° C., the treatment bath is likely to have cloudiness and suffer the generation of the sludge. The attempt to keep the chemical conversion bath at that temperature would require a great amount of energy; and this is economically disadvantageous.

EXAMPLES

Hereinafter, the present invention will be described in more detail with reference to examples without limiting the present invention to those examples. In Examples and Comparative Examples, “%” denotes “mass %” unless otherwise noted.

Example 1

An aqueous solution containing zirconium ions, aluminum ions and fluorine ions each with a concentration indicated in Table 1 was prepared, resulting in being a chemical conversion bath of Example 1. A source for zirconium ions was (NH₄)₂ZrF₆; a source for fluorine ions was HF. A treatment target was an aluminum can without its lid obtained by subjecting an aluminum alloy (A3004) plate to DI processing. The chemical conversion bath with pH, a treatment temperature and a treatment time each indicated in Table 2 was employed to perform a chemical conversion treatment. The pH indicated in Table 2 means the pH at 25° C.

Examples 3, 5, 7 and 9

A solution that contained zirconium ions, aluminum ions and fluorine ions and also contained phosphoric acid, phosphorous acid, hydrogen peroxide (H₂O₂) each with a concentration indicated in Table 1, was prepared, resulting in a chemical conversion bath of Example 3, 5, 7 or 9. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the treatment conditions indicated in Table 2.

Example 2

The chemical conversion bath of Example 1 was supplied with 0.1% of a replenishing agent A containing 20 g/L of zirconium ions, 20 g/L of fluorine ions, and 20 g/L of nitric acid, resulting in being a chemical conversion bath of Example 2. Sources for the individual components were the same as those used in Example 1. The above-mentioned supplying resulted in giving amounts of the components in the chemical conversion bath as indicated in Table 1. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the treatment conditions indicated in Table 2.

Example 4

The chemical conversion bath of Example 3 was supplied with 0.1% of a replenishing agent B containing 10 g/L of zirconium ions, 10 g/L of fluorine ions, 10 g/L of phosphoric acid, and 20 g/L of nitric acid, resulting in being a chemical conversion bath of Example 4. Sources for the individual components were the same as those used in Example 1. The above-mentioned supplying resulted in giving amounts of the components in the chemical conversion bath as indicated in Table 1. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the individual treatment conditions indicated in Table 2.

Example 6

The chemical conversion bath of Example 5 was supplied with 0.1% of a replenishing agent C containing 10 g/L of zirconium ions, 10 g/L of fluorine ions, 10 g/L of phosphoric acid, 10 g/L of phosphorous acid, and 20 g/L of nitric acid, resulting in being a chemical conversion bath of Example 6. Sources for the individual components were the same as those used in Example 1. The above-mentioned supplying resulted in giving amounts of the components in the chemical conversion bath as indicated in Table 1. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the treatment conditions indicated in Table 2.

Example 8

The chemical conversion bath of Example 7 was supplied with 0.1% of a replenishing agent D containing 10 g/L of zirconium ions, 10 g/L of fluorine ions, 10 g/L of phosphoric acid, 10 g/L of hydrogen peroxide, and 20 g/L of nitric acid, resulting in being a chemical conversion bath of Example 8.

Sources for the individual components were the same as those used in Example 1. The above-mentioned supplying resulted in giving amounts of the components in the chemical conversion bath as indicated in Table 1. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the treatment conditions indicated in Table 2.

Example 10

The chemical conversion bath of Example 9 was supplied with 0.1% of a replenishing agent E containing 10 g/L of zirconium ions, 10 g/L of fluorine ions, 10 g/L of phosphoric acid, 10 g/L of phosphorous acid, 10 g/L of hydrogen peroxide, and 20 g/L of nitric acid, resulting in being a chemical conversion bath of Example 10. Sources for the individual components were the same as those used in Example 1. The above-mentioned supplying resulted in giving amounts of the components in the chemical conversion bath as indicated in Table 1. The chemical conversion treatment was performed under the same treatment conditions as in Example 1 except having any changes in the treatment conditions indicated in Table 2.

TABLE 1 Chemical conversion bath Treatment liquid Additive component Phosphoric Phosphorous Electric Zr Al F acid acid H₂O₂ conductivity F/Al (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mS/cm) ratio Example 1 180 100 180 — — — 2.5 1.6 2 200 100 200 — — — 2.6 2.0 3 40 100 190 40 — — 1.9 1.9 4 50 100 200 50 1.9 2.0 5 50 100 200 50 50 — 2.6 2.0 6 60 100 210 60 60 — 2.7 2.1 7 40 100 190 40 — 40 2.5 1.9 8 50 100 200 50 — 50 2.5 2.0 9 40 100 200 40 50 40 2.3 1.9 10 50 100 210 50 60 50 2.6 2.0 Comparative 1 50 100 500 50 — — 3.2 5.0 Example 2 50 100 150 50 — — 2.2 1.5 Replenishing agent E C Zr 10 g/L Zr 10 g/L D F 10 g/L B F 10 g/L Zr 10 g/L Phosphoric Zr 10 g/L Phosphoric F 10 g/L acid 10 g/L A F 10 g/L acid 10 g/L Phosphoric Phosphorous Zr 20 g/L Phosphoric Phosphorous acid 10 g/L acid 10 g/L F 20 g/L acid 10 g/L acid 10 g/L H₂O₂ 10 g/L H₂O₂ 10 g/L Nitric acid Nitric acid Nitric acid Nitric acid Nitric acid 20 g/L 20 g/L 20 g/L 20 g/L 20 g/L Example 1 — — — — — 2 Example — — — — 1 +0.1% 3 — — — — — 4 — Example — — — 3 +0.14 5 — — — — — 6 — — Example — — 5 +0.1% 7 — — — — — 8 — — — Example — 7 +0.1% 9 — — — — — 10 — — — — Example 9 +0.1% Comparative 1 — — — — — Example 2 — — — — —

TABLE 2 Evaluation result Chemical conversion Boiling Adhesiveness treatment conditions water Primary Temperature Time corrosion OT bending Secondary pH (° C.) (Second) resistance test (mm) 1 mm grid 1 mm grid Example 1 3.3 40 20 B 0.1 100 100 2 3.1 40 20 A 0.1 100 100 3 3.3 40 20 A 0.1 100 100 4 3.1 40 20 A 0.1 100 100 5 3.0 40 20 A 0.1 100 100 6 2.9 40 20 A 0.1 100 100 7 3.0 40 20 A 0.1 100 100 8 2.9 40 20 A 0.1 100 100 9 3.0 40 20 A 0.1 100 100 10 3.9 40 20 A 0.1 100 100 Comparative 1 3.0 40 20 C 0.3 90 95 Example 2 3.0 40 20 C 0.4 92 97

An aluminum can that was a treatment target of the chemical conversion bath of Examples and Comparative Examples was pretreated in the following manner. First, the aluminum can was spray-treated with a commercially-available acidic cleaner (SURFCLEANER NHC260 manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at 75° C. for 60 seconds to remove therefrom lubricating oil and smut. The resultant aluminum can was spray-washed with tap water for 15 seconds. The resultant aluminum can that was a treatment target was sprayed with the chemical conversion agent composition according to the chemical conversion bath of any of Examples and Comparative Examples under conditions indicated in Table 1. The resultant aluminum can was spray-washed with tap water for 15 seconds and with deionized water for 5 seconds, and thereafter dried at 200° C. for 3 minutes. In this way, the treated container of any of Examples and Comparative Examples for evaluation tests shown below was prepared.

[Test of Corrosion Resistance in Boiling Water]

A can bottom cut out from the treated container of any of Examples 1 to 10 and Comparative Examples 1 and 2 was soaked in boiling tap water at 100° C. for 30 minutes. The degree of blackening that could be observed at the outer surface of the can bottom was visually evaluated on the basis of the evaluation criterion shown below. Results of the evaluation are indicated in Table 2. The mark “A” denotes the passing of the test, while the marks B and C denote the failing of the test. A: No blackening

B: Slight blackening C: Pronounced blackening

The treated container of any of Examples 1 to 10 and Comparative Examples 1 and 2 was dried and cut to give a test piece. The test piece was coated with an epoxy acrylic coating material by using a bar coater so that the dried coating film would have a thickness of 5 μm, and thereafter stoved to be cured in an atmosphere of 250° C. for 3 minutes. The resultant coating film formed by the stove-curing was subjected to a test of coating film adhesiveness indicated below.

[Primary Adhesiveness Test]

The coating film obtained above was subjected to a primary adhesiveness test, which was OT bending test. The portion of the coating film that was bent and lifting was removed by using an adhesive tape, and thereafter the peeling width at both sides of the bent portion was measured. When the peeling width was not more than 0.1 mm, this was rated as the test being passed. When the peeling width was more than 0.1 mm, this was rated as the test being failed. Results are indicated in Table 2.

Similarly, a 1 mm cross-cut adhesiveness test with reference to the old JIS K 5400 was performed as the primary adhesiveness test. In the cross-cut adhesiveness test, one hundred grids each with a 1 mm width were formed on the coating film by using a utility knife, and thereon an adhesive tape was attached and then detached. At this time, the number of grids still having the coating film was counted. When the number of grids still having the coating film was one hundred, this was rated as the test being passed. When that did not occur, this was rated as the test being failed. Results are indicated in Table 2.

[Secondary Adhesiveness Test]

The coating film obtained above was soaked in boiling water for 30 minutes, and the resultant coating film was subjected to a secondary adhesiveness test, which was a 1 mm cross-cut adhesiveness test, as was the case with the foregoing test. When the number of grids still having the coating film was one hundred, this was rated as the test being passed. When that did not occur, this was rated as the test being failed. Results are indicated in Table 2.

The comparison between Examples 1 to 10 and Comparative Example 1 have revealed that the aluminum substrates treated with the chemical conversion baths of Examples 1 to 10, as compared with the aluminum substrate treated with the chemical conversion bath of Comparative Example 1, were superior in the results of the boiling water corrosion resistance and adhesiveness tests. These results have verified that controlling F/Al in the chemical conversion bath to be not more than 4.5 led to the provision of the aluminum substrate with a chemical conversion coating high in corrosion resistance and adhesiveness.

The comparison between Examples 1 to 10 and Comparative Example 2 have revealed that the aluminum substrates treated with the chemical conversion baths of Examples 1 to 10, as compared with the aluminum substrate treated with the chemical conversion bath of Comparative Example 2, were superior in the results of the boiling water corrosion resistance and adhesiveness tests. These results have verified that controlling F/Al in the chemical conversion bath to be not less than 1.8 led to the provision of the aluminum substrate with a chemical conversion coating high in corrosion resistance and adhesiveness.

Accordingly, it has been verified from the foregoing that controlling F/Al in the chemical conversion bath to be kept in a range from 1.8 to 4.5 enabled the chemical conversion bath to keep being capable of forming the chemical conversion coatings with high corrosion resistance. 

1. A method for replenishing an aluminum metal chemical conversion bath with a replenishing agent, wherein the replenishing agent comprises a zirconium salt and/or a titanium salt, and an effective fluoride, and wherein the replenishing agent is supplied so that the ratio F/Al of the fluorine ion concentration (mg/L) with respect to the aluminum ion concentration (mg/L) in the aluminum metal chemical conversion bath is 1.8 to 4.5.
 2. The method according to claim 1 for replenishing an aluminum metal chemical conversion bath, wherein the replenishing agent further comprises at least one kind selected from the group consisting of phosphoric acid, phosphorous acid and hydrogen peroxide.
 3. The method according to claim 1 for replenishing an aluminum metal chemical conversion bath, wherein the aluminum metal chemical conversion bath comprises a zirconium salt and/or a titanium salt; an effective fluoride; at least one kind selected from the group consisting of phosphoric acid, condensed phosphoric acid and salts thereof; and at least one kind selected from the group consisting of phosphorous acid, hypophosphoric acid and salts thereof.
 4. The method according to claim 1 for replenishing an aluminum metal chemical conversion bath, wherein the replenishing agent is supplied such that the chemical conversion bath has a pH in a prescribed range so as to give the F/Al ranging from 1.8 to 4.5.
 5. The method according to claim 1 for replenishing an aluminum metal chemical conversion bath, wherein the replenishing agent is supplied such that the chemical conversion bath has an electric conductivity in a prescribed range so as to give the F/Al ranging from 1.8 to 4.5.
 6. The method according to claim 1 for replenishing an aluminum metal chemical conversion bath, wherein a treatment target of the aluminum metal chemical conversion bath is an aluminum beverage can. 